1. Field of the Invention
The present invention relates to an autostereoscopic display. Such a display may comprise an autostereoscopic three dimensional (3D) display and maybe used, for instance, in 3D television, medical imaging, computer games, telephony, scientific visualisation, virtual reality and office automation equipment.
2. Description of the Related Art
A known type of autostereoscopic 3D display is shown in FIG. 1 of the accompanying drawings. The display comprises a diffuse back light 1 disposed behind a spatial light modulator (SLM) 2, for instance in the form of a liquid crystal display (LCD). The SLM 2 comprises an array of picture elements (pixels), for instance as disclosed in European Patent No. 0 625 861 in which the pixels are arranged in columns such that adjacent columns are substantially contiguous with each other in the lateral or horizontal direction.
A parallax optic 3, for instance in the form of a lenticular screen as illustrated diagrammatically in FIG. 1, is disposed in front of the SLM 2. Each parallax element 6 of the parallax optic 3 is aligned with a respective pair of pixel columns of the SLM 2. The pixel columns are controlled so as to display alternating vertical strips of left and right two dimensional (2D) images for the left and right eyes, respectively, of an observer. For instance, the pixel indicated at 4 displays an element of a left eye image whereas the pixel indicated at 5 displays an element of a right eye image.
Light from the columns including the pixels 4 and 5 is imaged by the associated parallax element 6 in a first lobe 7. Light from adjacent pixel columns indicated at 8 and 9 is imaged by the parallax element 6 into adjacent lobes 10 and 11, respectively. Further, light from the next columns indicated at 12 and 13 is imaged by the parallax element 6 into the further lobes 14 and 15.
In order to provide a viewpoint corrected display such that each eye of an observer sees the same image across the whole of the display, the pitch of the parallax elements of the parallax optic 3 is slightly less than twice the pitch of the pixel columns of the SLM 2. Alternatively the parallax optic may be disposed between the diffuse backlight 1 and the SLM 2, in which case the pitch of the parallax elements of the parallax optic should be slightly greater than twice the pixel column pitch.
This creates viewing zones which are repeated in several lobes. Provided the left and right eyes of an observer are located in the left and right viewing zones, respectively, of one of the lobes, the left eye sees only the 2D image intended for viewing by the left eye and the right eye sees only the 2D image intended for viewing by the right eye across the whole of the display. The widest parts of the viewing zones are referred to as viewing windows and are located in a common plane as indicated at 16. The viewing windows 16 are formed at the intended viewing distance from the display.
Provided the left and right eyes of an observer remain in the left and right eye viewing zones, respectively, the observer views the display orthoscopically and sees the correct 3D image. Such viewing zones may be referred to as orthoscopic viewing zones and viewing window positions for orthoscopic viewing are indicated at 17 to 21. However, if the left and right eyes of the observer are located in right and left viewing zones, respectively, the observer sees a pseudoscopic image. Pseudoscopic viewing window positions are indicated at 22 to 25 in FIG. 1. Pseudoscopic images create problems because they often appear to have some depth despite the depth information being misleading or false. It is not, therefore, always obvious that the observer is in the wrong location. Further, pseudoscopic viewing is known to cause headaches and other symptoms of visual strain.
Further, as the viewer moves laterally, the eyes may move to a position where the content viewed by, for example, the right eye, contains a significant portion of the left eye lobe. This again leads to a non-ideal view position which is known to cause headaches and other symptoms of visual strain.
“Proceedings of Third International Display Workshop”, volume 2, Nov. 27-29, 1996 E. Nakayama et al, 1996 International Conference Centre, Kobe, Japan discloses a 3D indication for assisting an observer to find the proper viewing region of an autostereoscopic 3D display of the type shown in FIG. 1 of the accompanying drawings. The indicator is shown in FIG. 2 of the accompanying drawings and comprises a light-proof box 26 having a front slit 27 and containing light emitting diodes (LED) 28 to 32. The LEDs 28, 30 and 32 emit green light whereas the LEDs 29 and 31 emit red light. The size of the slit 27 and the geometry of the LEDs 28 to 32 with respect to the slit 27 are such that, when the eyes of the observer are located in the orthoscopic positions 17 to 21, light from the LEDs 32 to 28, respectively, can be seen through the slit 27. Thus, when the observer's eyes are in one of the orthoscopic positions 17 to 21, either only a green LED or only a red LED is visible. When the observer moves away from the orthoscopic positions, light from both a green LED and a red LED becomes visible. The observer must therefore position himself so that he can see only light of a single colour through the slit 27 of the indicator.
The indicator is made as a separate device from the autostereoscopic display and therefore requires correct alignment during manufacture in order to ensure that the regions where only a single colour is visible align correctly with the orthoscopic positions within the viewing windows. Such alignment is time-consuming and troublesome and therefore substantially adds to the cost and complexity of manufacture. Further, the optical system of the indicator is different from the optical system of the display itself. Thus, the indicator only provides correct identification of orthoscopic viewing positions at and very close to the plane containing the viewing windows. If the observer moves significantly outside this plane, the indicator no longer provides a correct indication of whether the observer is in an orthoscopic or non-orthoscopic position. Also, because of differences between the optical system of the indicator and the optical system of the display, the indicator provides an indication which is independent of the performance of the display optical system. Thus, even if the indicator is correctly aligned with the display, an observer may receive a false indication of being in an orthoscopic position when, in fact, imperfections in the display optical system are such that the observer is in an inappropriate viewing position.
GB 2 252 175 discloses an autostereoscopic display of the parallax barrier type. When a viewer moves out of the orthoscopic viewing region, the image which is visible to the viewer changes. Lateral movements causes the perceived image to darken whereas longitudinal movement results in vertical stripes being superimposed on the image. These image changes result from the parallax barrier structure of the display.
WO 94/24601 also discloses an autostereoscopic display in which the perceived image changes when the viewer moves outside the orthoscopic viewing region. In this case, the perceived image becomes monoscopic immediately the viewer leaves the orthoscopic viewing zone so as to avoid pseudoscopic viewing.
EP 0 860 728 and GB 2 321 815 disclose an autostereoscopic 3D display, as shown in FIGS. 3 and 4 of the accompanying drawings, which differs from that shown in FIG. 1 in that it includes a viewer position indicator (VPI) arrangement shown in FIG. 4. This arrangement comprises part of the backlight 1, part of the SLM 2 and part of the parallax optic 3. As shown in FIG. 3, the SLM 2 has an image portion 2a for displaying two 2D stereoscopic images as interlaced vertical strips on alternating columns of pixels with each parallax element 6 being optically aligned with an adjacent pair of pixel columns. Left and right viewing zones are formed in the lobes 7, 10, 11, 14 and 15 but only the orthoscopic viewing positions 17, 19 and 21 are intended for use by an observer. Thus, the orthoscopic positions 18 and 20 shown in FIG. 1 are not intended for use.
The viewer position indicator arrangement is formed by an upper strip of the backlight 1, a signalling portion 2b comprising one or more upper rows of pixels of the SLM 2, and a upper portion 3a of the parallax optic 3. The pixels shown in FIG. 4 are operated in horizontal pairs so as to act as pixels such as 30 and 31 having twice the horizontal extent and twice the pitch of the pixels shown in FIG. 3 and used for displaying the stereoscopic image. The upper portion 3a of the parallax optic 3 comprises a portion whose parallax elements 32 have twice the horizontal pitch of the parallax elements 6 shown in FIG. 3. Pixels such as 30 (shown unshaded) are controlled so as to provide a bright image and alternate laterally with pixels such as 31 (shown shaded) which are controlled so as to provide a dark image. In particular, the pixels 30 are substantially transparent whereas the pixels 31 are substantially opaque.
Each parallax element 32 is aligned with a respective parallax element 6. The pixels 30 and 31 and the parallax elements 32 cooperate to provide a bright image in the lobes 10 and 11 and a dark image in the lobes 7, 14 and 15. Thus, when an observer is located at the orthoscopic positions 17, 19 and 21 in the viewing windows 16, the viewer position indicating arrangement appears dark. As the observer moves from an orthoscopic position such as 19 to a pseudoscopic position such as 23, light from the viewer position indicating arrangement becomes visible, for instance to the right eye of the observer, thus indicating to the observer that he has moved from an orthoscopic position to a pseudoscopic position. If just one eye sees light from the viewer position indicating arrangement, the brain registers this as image data. The display does not, therefore, require both eyes of the observer to see light from the arrangement in order to work. Thus, provided the observer moves to a position where no light is visible from the viewer position indicating arrangement, he will remain in an orthoscopic position such as those indicated at 17, 19 and 21.